Sage II - Boot Errors; CRT Problems; LED Blinking; LED Green

SAGE
II SERVICE
KIT
CPU
BOARD
CIRCUIT
DESCRIPTIONS
PAGE
3
OF
SCHEI'IATIC
DIAGRAI'{S
(cont)
RAU
CONTN.OL
SIGNALS
The
wrlte
enable
signals
are
produced
by
U41,
U40 and
RN3.
LDS+
from
U44-16
of
page
I
and
BRW- from
37-4
also
on
page
I are
comblned
at
U4l
a
7/+LS08
ANn
gate"
The
output
of
U41-11
ls
lnput
at
U40
pins
Z
and
4
and
pro<luces
the lndependently
buf f
ered low
byte write
enable
s
ignals
LI^10
and
l,Wl '
$funilartr-y,
the
upper
byte
wriLe
enable
signals
In^10 and
UWI
are
procluced
at
U41-8 by
UDS+ upper
data strobe
from
U44-18
page
I
wh{ch
ls
logical
AND'd
with
BRW-
brrff,ered
read
/
write.
The
RAH
data
bus
control
slgnals
RRDI-
and
RWR- are
generated
from
RAM+
and
the buffered
read
/
wrlte
llnes,
BRW+
from
U37-2
page
1
is
combined
wlth
RAM+ at pins
1
and
2
of
U4I
74LS08 AIID
gate
making
RRDI-
ar
pin
3
active
high
for
a
read
cycle.
BRW- at
U32-12 AND RAI.{+
at
U32-13 make
Ri'fR*
actLve
low
for
a
wrlte
cycle
at
pln
11
of
U32
74LS00
NAND
gate.
All of
the
slgnals
on the
right
side of
schematic
page
3
except
BE- and
RAM+ are
RAtl
control
signals
and
go
to
page
4. BE-
goes
to
U52-g
page
I
and
RAI+
goes
to
U52-9
page
l.
B{IS
BR.ROR
GENERATION
FOR
IONEXISTANT
I{EUORY
LOCATIONS
Whenever
a
memory
locatlon
ls
addressed
which
is
not
a
decoded
address
in
the
SAGa
memory
map there
j-s
no
DTACK-
generated
which
causes
a
bus
timeout
error
as
descri"bed
above.
This allows
an orderly
recovery
from
the
addressing
of
any
nonexistent
memory locatlons.
generated
for
a1"1
locatlons
ln
the
SAGE rr
memory map.
A
DTACK- ls
If Lhe
system
had
onl-y
12BK and
a
location
between
l28K
&
5l2K
were
addressed,
there
roould
be no
indication.
To
solve
this
problen
the
bank
enables
for
banks
0, 1
,
2, &
3
are
f
ed
through
an nonl-nverting
open
collector
buffer
(U48)
to
the
bus
error
lnput
of
the
processor
through
a
dlp
shunt.
I4lifh
the
proper
connections
in
the dip
shunt
the
addreritng
of
any locati"on
in
hanks
1, 2,
or
3 can
cause
a bus
error
indlcatlng
"rt
i.nvalld
memory
address.
63